DATA TRANSMISSION

IntroductionData into a computer (via a keyboard) is encoded by the electronics within the keyboard into an equivalent binary-coded pattern using standard coding schemes:Two most common schemes:EBCDIC (Extended Binary Coded Decimal Interchange Code): 8-bit codeASCII ((American Standards Committee for Information Interchange): 7-bit code
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DATA TRANSMISSION DATATRANSMISSION 1Introduction Dataintoacomputer(viaakeyboard)is encodedbytheelectronicswithinthe keyboardintoanequivalentbinarycoded patternusingstandardcodingschemes: Twomostcommonschemes: EBCDIC(ExtendedBinaryCodedDecimal  InterchangeCode):8bitcode ASCII((AmericanStandardsCommitteefor  InformationInterchange):7bitcode 2BitTransmission Parallelmode:usesseveralwires,eachwire sendingonebitatthesametimeasthe others. Serialmode:sendsbitbybitoverasingleline Serialmodeisslowerthanparallel,butcan beusedoverlongerdistancesbecausethe bitsstayintheordertheyweresent,while bitssentinparallelmodetendtospreadout overlongdistances. 3ParallelTransmission 4SerialTransmission 5CommunicationModes Simplex:Usedwhendataistobetransmitted inonedirectiononly HalfDuplex:Usedwhenthetwo interconnecteddeviceswishtoexchange informationalternately(onlyonedevicecan transmitatatime) FullDuplex:Usedwhendataistobe exchangedbetweenthetwoconnected devicesinbothdirectionssimultaneously 6TransmissionModes Forthereceivertodecodeandinterpretbit patterncorrectly,itmustbeabletodetermine Thestartofeachbitcellperiodbit/clock  synchronization Thestartandendofeachelements(character/  byte)character/bytesynchronization Thestartandendofeachcompletemessage  blockframesynchronization 7TransmissionModes Asynchronoustransmission: Transmitterandreceiverclocksare independent Synchronoustransmission:Transmitter andreceiverclocksaresynchronized 8AsynchronousTransmission 9AsynchronousTransmission Inasteadystream,intervalbetweencharactersis uniform(lengthofstopelement) Inidlestate,receiverlooksfortransition1to0 Thensamplesnextsevenintervals(charlength) Thenlooksfornext1to0fornextchar Simple Cheap Overheadof2or3bitsperchar(~20%) Goodfordatawithlargegaps(keyboard) 10SynchronousTransmission Blockofdatatransmittedwithoutstartor stopbits Clocksmustbesynchronized Canuseseparateclockline Goodovershortdistances  Subjecttoimpairments  11ErrorControlandFlowControl Errorcontrol:schemesandprocedures todetectandcorrecttheoccurrenceof transmissionerrors Flowcontrol:Thecontroloftheflowof informationbetweentwoDTEs 12AsynchronousTransmission TransmissioncontrolcircuitswithinDTEmust performthefollowingfunctions: Paralleltoserialconversion(PISO)ofeach  character/byteinpreparationforitstransmission Serialtoparallelconversion(SIPO)ofeach  receivedcharacter/byteinpreparationforits storageandprocessing Ameansforreceivertoachievebit,characterand  framesynchronization Thegenerationofsuitableerrorcheckdigitsfor  errordetection 13AsynchronousTransmission Bitsynchronization Startbit&stopbit  Receiverclocksamplestheincomingsignalas  neartothecenterofthebitcellaspossible Charactersynchronization Numberofbits/character  Framesynchronization Controlcharacter:STX&EXT  14AsynchronousTransmission 15Asynchronoustransmission 16AsynchronousTransmission 17SynchronousTransmission Blockofdatatransmittedwithoutstartor stopbits Eachframeistransmittedasa contiguousstreamofbinarydigits Clocksmustbesynchronized 18SynchronousTransmission Bitsynchronization Clockencodingandextraction  DigitalPhaselockloop(DPLL)  Hybrid  Framesynchronization Characteroriented  ...